This invention relates in general to electromagnetic clutch assemblies and in particular to a method of manufacturing a rotor for use in an electromagnetically actuated friction clutch.
Clutches are well known devices which are commonly used in machinery to selectively connect a source of rotational power to a rotatably driven mechanism. A basic clutch structure includes an input member connected to the source of rotational power, an output member connected to the rotatably driven mechanism, and means for selectively connecting the input member to the output member for concurrent rotation. When the means for selectively connecting is engaged, the input member is connected to the output member so as to rotatably drive the mechanism. When the means for selectively connecting is disengaged, the input member is disconnected from the output member, and the mechanism is not rotatably driven. Many different types of clutches are known in the art for accomplishing this general purpose.
In some clutches, the input member and the output member are axially fixed in position relative to one another. An armature is connected to the output member for rotation therewith and for axial movement relative thereto. The armature is axially movable between a disengaged position, wherein it is spaced apart from the input member, and an engaged position, wherein it frictionally engages the input member. The armature is normally maintained in the disengaged position, wherein it does not frictionally engage the input member and, therefore, is not rotatably driven thereby. When moved to the engaged position, however, the armature frictionally engages the input member so as to be rotatably driven. Friction clutches of this general type are well known in the art.
In some friction clutches, an electromagnet is used to cause selective movement of the armature between the engaged and disengaged positions. Electromagnetically actuated friction clutches of this general type operate on the principle that a magnetic field which is created about a component formed from a magnetically permeable material will exert a mechanical force on a nearby component. This mechanical force will urge the component to move to a position of minimum resistance relative to the flow of magnetic flux (lines of force) generated by the magnetic field, usually referred to as a position of minimum reluctance. Thus, in electromagnetically actuated friction clutches, the input member and the armature are both formed from a magnetically permeable material. When the electromagnet is energized, the electromagnetic field generated thereby attracts the armature toward the input member. As a result, the armature is moved from the disengaged position to the engaged position, connecting the input shaft to the output shaft and causing the driven device to be rotatably driven by the source of rotational power.
In a typical electromagnetically actuated friction clutch, the input member is embodied as an annular rotor which is generally U-shaped in cross section. Such a rotor includes an outer circumferential wall, a concentric inner circumferential wall, and a pole face extending radially therebetween. In many instances, a pulley is wrapped about the outer circumferential wall of the pulley to provide a driving connection between the source of rotational power and the rotor. When the clutch is in the disengaged position, the pole face of the rotor is separated from the armature by a relatively small air gap. Frequently, the pole face of the rotor (and armature also) can be divided into at least two magnetic poles by recesses or slots. The discrete poles cause the magnetic flux generated by the energized electromagnet to jump back and forth several times across the air gap separating the rotor and the armature. As is well known, this magnetic flux discontinuity structure, or more simply flux break, provides the magnetic attraction between the rotor and the armature.
In the past, the rotor has been manufactured using a combination of conventional metal working and machining processes. However, known rotor manufacturing processes suffer from several drawbacks. In particular, it has been found that known manufacturing processes require a relatively large number of such metal working and machining processes which are time consuming and, therefore, inefficient. Also, known manufacturing processes require the removal of a relatively large amount of material, which is also inefficient. Third, known manufacturing processes have been found to create internal stresses within the rotor at undesirable locations, thereby reducing the strength of the rotor. Thus, it would be desirable to provide an improved method for manufacturing a rotor for use in an electromagnetic friction clutch which addresses these problems.